Calculate: \left( 1-\frac{1}{2} \right)\times \left( 1-\frac{1}{3} \right)\times \left( 1-\frac{1}{4} \right)\times \left( 1-\frac{1}{5} \right)=
\frac{1}{2}\times \frac{2}{3}\times \frac{3}{4}\times \frac{4}{5}=\frac{1}{5}
